with straightforward one-pass .tex to .pdf conversion.
Comparing to .eps inclusion done by GhostScript (or epstopdf) calls, GeX offers much better performance and output quality. Inline PostScript inclusion, on the other hand, is a totally new feature: this is this a feature that only VTeX/GeX supports. The advantage of GeX over GhostScript image embedding is apparent from the following pictures:
| GeX | 
|
| GS | 
|
Here we include the same .eps file with both GeX and GhostScript (a new \special{GS+}/\special{GS-} was added to VTeX just for the sake of this comparison). Besides being cleaner, the first picture (GeX output) takes less space and takes less time to compile.
Note: The images in this HTML version of documentation are cropped and magnified; see the PDF documentation for more juicy details.
Note: Three main differences between the pictures are: (1) GhostScript rasterizes fonts into bitmaps, GeX keeps them as Type1; (2) Color rendering done by GeX is identical to what would be produced by Acrobat but different by what is done by GhostScript; (3) some words for unclear reasons dissappeared from the GhostScript output, they are present in both GeX and Distiller outputs. "Running" is set in different fonts: the original picture did not provide the font used for this word; the substitution performed by GeX and GhostScript were different and neither is at fault here.
For reference, this is the VTeX code used to place the pictures:
\hbox to \textwidth{
||\includegraphics[width=5cm]{olympics.eps} \hss
\special{GS+}%
\includegraphics[width=5cm]{olympics.eps}%
\special{GS-}%
||%
}
The .eps inclusion is likely to be the main initial application of GeX. However, in our view it is the inline PostScript which would lead to new and interesting applications.
The GeX name [pronounced g-e-k-s] stands for Graphics EXtensions.
While the current extensions are generally compatible with the
PostScript language, GeX is intended to be a TeX-resident extension,
not an Acrobat clone. Even in the current implementation there are facilities
for communication between TeX and PostScript; these facilities are likely
to be further developed. While it is our intention to stay
PostScript-compatible to a degree needed for .eps and inline
PostScript support we envision further enhancing GeX with features that
are decisively non-PostScript.
To enable GeX, use the
-ox
switch on the VTeX command line. GeX initialization will take place only when GeX is explicitly called for the first time. Notice that GeX works only in the PDF backend mode; in other modes the switch will be ignored.
Note: The -ox2 switch will initialize GeX in Level II PostScript mode.
GeX initialization would fail if GeX cannot locate the base fonts.
GeX requires the base-13 fonts to be available. Make sure that the aliasing.pst file lists them and that the .tfm files for them are in tfm.lib.
The base-13 fonts are the 4 variants of Times, Helvetica, and Courier each,
plus the Symbol font.
GeX currently supports a large subset of PostScript, including most of Level I implementation and some Level II operators.
Since not the full PostScript operator set is supported, it is possible (and even easy) to write a valid PostScript code which will be rejected by GeX; on the other hand, the supported subset includes all the ``practically'' used operators, so GeX would handle correctly most .eps that do appear in vivo. Testing of GeX on a large random set of .eps files downloaded from Internet shows that GeX correctly handles more than 99% of them. The supported instruction set at this time consists of 221 PostScript operators and several extension operators described below.
Note that if you are going to use GeX primarily for inclusion of ready-made .eps files, you should use a high-level package like graphics rather than VTeX's \special's.
In GeX mode, VTeX allows to precede a \special with the \immediate command. \immediate \special's are passed to GeX right away, while TeX is still doing formatting. At this time there is no way to use the .pdf code that could be generated during the execution of an \immediate \special; however, the GeX kernel can be used for computations; and the results of such computation can be passed back to TeX. One practical example of this is the letterspacing implementation.
To report the results from GeX to TeX, set the \psconsole integer parameter to a number between 0 and 255:
\psconsole=100
This instructs GeX to write the output to the \toks### register rather then to the console (### is the number passed via \psconsole. By default, \psconsole is set to -1 and GeX output goes to the .log file; when \psconsole is in the 0--255 range, the output goes to the corresponding \toks register.)
The output is always appended to \toks; multiple outputs from GeX get concatenated within the \toks register. The only ways to clear the \toks register are via a TeX assignment
\toks100={}
or by restoring the register on a TeX group closing.
Notice further that you should use the PostScript print operator to place information into a \the\toks register. This is because the other output operators (=, pstack) append newline characters and the resulting contents will be difficult to parse in TeX. (Also, the actual format of the output of these operators may change in the future versions of GeX.) Since print allows only string arguments, you may need to use the cvs operator to convert other PostScript types to strings (see an example below).
If you intend to retrieve information from GeX with \immediate\special, make sure to flush GeX output once at the beginning:
\immediate\special{pS: }
The reason for this is that GeX is initialized when a first \special{pS:...} is encountered; during its first-time initialization it produces some output which normally goes to the .log file and you do not want to be appended to the \toks variable. Supplying an empty call to GeX forces it to be initialized and the initialization output to be written to the .log file.
Here is a small example of using GeX inline:
\documentclass{article}
\begin{document}
\immediate\special{pS: \the\year\space srand}
% This also will initialize GeX
\def\rand{%
\immediate\special{pS: }%
\psconsole 100
\immediate\special{pS: rand 10 string cvs print}%
The number is = \the\toks100.
\psconsole -1
\toks100={}
}
\rand\par\rand\par\rand\par
\end{document}
[You may want to cut out the text of this example and try it yourself.]
GeX version 6.3 supports these additional extensions operators:
Unfortunately, both the PDF standard and Adobe's implementation are not bug-free. Some of the more interesting bugs are described here.
Near-degenerate matrix transforms cause a serious problem with the Acrobat's 16-bit computational limit. It can be shown that the problem is not solvable correctly in general; and Adobe Acrobat Distiller would fail on degenerate transforms.
The example file
% lwid.ps
0 0 moveto
gsave 100 200 lineto 2 3 scale 1 0 0 setrgbcolor stroke grestore
gsave 200 100 lineto 0.5 0.3 scale 0 1 0 setrgbcolor stroke grestore
gsave 200 200 lineto 0 0 1 setrgbcolor
[0.186718 -0.565306 0.873838 -2.64563 0 0] setmatrix
stroke grestore
showpage
should produce three lines from the origin. Distiller, however, will miss
the blue line. GeX, on the other hand, will produce correct output:
Near-degenerate matrices are not a perverted abberation: they tend to be generated by some common software, especially the CorelDraw. The particular set of numbers in the source above came from a Corel example.
While GeX does the work correctly in all cases, some distortion in the line widths is possible and is not avoidable.
| 
|
The nature of the problem is a bug (or feature) in the Freehand
adjustment
code which does not bother to check for the device matrix and assumes
that it corresponds to the output pixel resolution of 300 dpi or higher
(which would imply a device matrix [N 0 0 N .. ..]; N>4). However, the
GeX device matrix is chosen to be an identity, to avoid extra rounding
by TeX's->GeX's coordinate translation. This causes
extremely coarse coordinate rounding.
To avoid this problem, set the \GeXinnerscale counter to
at least 4. The example above, for example, was produced with
\hbox to \textwidth{
||\includegraphics[width=5cm]{gears.eps} \hss
GeXinnerscale=4%
\includegraphics[width=5cm]{gears.eps}
||%
}
Notice that the Level II strokeadjust operator does not cause a problem since it is totally ignored by GeX.
All examples below will letterspace with extra 2-pt space.
Thus,
\immediate\special{pS: /k 2 def}%
Notice that \immediate\special is not normal TeX: it causes
a backend special to be evaluated right away, rather than waiting for
the output cycle. Let
\def\forcefont{\hbox to 0pt{\phantom{!}}}
\def\as#1{\forcefont\special{pS: k 0 (#1) ashow}}
A first attempt is to simply plug-in ashow:
Letterspacing: \as{Letter-spaced text here.}!
to obtain
does not work very well: the exclamation mark overlaps the L. Indeed, there is no way TeX would know how much space the \special would need.
Here is a macro that will measure the required width:
\newdimen\tmpz
\def\sw#1{%
\forcefont
\psconsole 255
\immediate\special{pS: (#1) dup stringwidth pop exch length 1 sub k mul add
10 string cvs print}%
\message{Result=[\the\toks255]}
\tmpz=\the\toks255pt
}
We call GeX in the \immediate mode since we want to reuse
the result to set the string.
\sw{Letter-spaced text here.}
Now, it will work correctly:
Letterspacing: \hbox to \tmpz{\as{Letter-spaced text here.}\hss}!
Note: Of course, it makes more sense to write a single macro but this example is provided for illustration purposes only.
Note: Even more sense would be to build the output code in the \immediate phase and re-use it later (one call to GeX, rather than two); such a feature might be added later.
Note:
One possible pitfall: GeX executes a
save-restore pair on each emitted page. Thus it is important
to assure that no page breaks would occur in the middle of calls to GeX.
and expects post-processing to find and substitute the fonts. Instead of such
post-postprocessing, GeX ignores (processes, which is the same really)
this declaration, but requires
either explicit loading of needed fonts via the .loadfont extension
\special{pS: /cmr10 .loadfont}
(one such command for each required font) or enabling of the
autoloading feature via the .autofontload extension
\special{pS: 1 .autofontload}
These commands must be issued before a MetaPost-generated file is actually included.